1. Field of the Invention
The present invention relates to a device for measuring at least one parameter of a flowing fluid medium through a flow pipe.
2. Description of Related Art
Thus, in many processes, for example in the fields of process engineering, chemistry or machine construction, fluid media, especially gas masses (e.g. an air mass) having particular properties (such as temperature, pressure, flow velocity, mass flow rate, etc.) must be supplied in a defined manner. This includes in particular combustion processes, which run under controlled conditions.
An important example of an application is the combustion of fuel in internal combustion engines of motor vehicles, especially those including a subsequent catalytic exhaust gas purification, in which a specific air mass per unit time (air mass flow) must be supplied in a controlled manner. Various types of sensors are used to measure the air mass throughput. One sensor type known from the related art is the so-called hot film air mass meter (HFM), which is described in one specific embodiment in DE 196 01 791 A1, for example.
Such hot film air mass meters normally use a sensor chip having a thin sensor diaphragm, for example a silicon sensor chip. At least one heating resistor, surrounded by two or more temperature measuring resistors (temperature sensors), is typically disposed on the sensor diaphragm. In an air flow that is routed across the diaphragm there is a change in the temperature distribution, which in turn is detectable by the temperature measuring resistors and may be evaluated with the aid of a control and evaluation circuit. Thus it is possible, for instance, to determine an air mass flow from a difference in resistance of the temperature measuring resistors. Several other variants of this type of sensor are known from the related art, for example sensors that use porous sensor chips instead of diaphragms.
The known hot film air mass meters as well as other known devices for determining at least one parameter of fluid media normally have a chip carrier, onto which or into which the sensor chip is inserted. The chip carrier usually extends into the fluid medium, the chip carrier normally being developed such that when the sensor chip is inserted an essentially smooth surface is formed over which the fluid medium is able to flow without forming turbulences.
In the known hot film air mass meters, for example, the chip carrier is produced in that a sheet metal carrier is used for a control and evaluation electronics, on which a circuit carrier (for example a circuit board) is fastened. The chip carrier itself is normally fastened on the sheet metal carrier by a mounting process, for example by injection molding in an injection molding process.
Following the assembly of the circuit carrier, the sensor chips are then normally mounted on the chip carrier in additional process steps. For this purpose, an adhesive is normally introduced into a receptacle made of metal or plastic, the chip is taken out of a diced-up silicon wafer using an additional handling system, and the chip is positioned within the chip receptacle within the chip carrier.
Subsequently, the adhesive, which may be a silicone adhesive for example, is cured in an oven.
This known manufacturing method and the devices manufactured by them leave room for improvements, however. In particular, numerous individual steps are required for introducing the sensor chip into or onto the chip carrier, which increase the cost of the manufacturing process and thus of the end product or lower the profit margins. Another disadvantage is the fact that the curing of the adhesive in the oven in turn may damage the already assembled electronics and that prior to curing component tolerances may result in that the sensor chip slips out of place on the uncured adhesive due to a normally existing play of the sensor chip within the chip carrier or a depression of the chip carrier.